Gases represented by 1 and 2 in the given picture arerespectively
AOxygen, Carbon dioxide
CNitrogen, Carbon dioxide
DCarbon dioxide, Oxygen
Answer is D because at night plants take in oxygen and give out carbon-di-oxide whereas we humans always take in oxygen and give out carbon-di-oxide.
Sorry ,answer is A .I gave wrong explanation why .You have told arerespectively, so gas 1 is carbon dioxide and gas 2 is oxygen.You have given the order as 1 and 2 i.e. carbon dioxide and oxygen.So ,we will say it as 2 and 1 i.e oxygen and carbon dioxide .Hence answer is A.